Method of cracking oils



Jan. 1, 1924 J. cs. DAVIDSON METHOD OF CRACKING OILS Original Filed June 10, 1920 2 Sheets-Sheet 1 \N W an newton Jan. 1, 1924 1 ,479,653

J. G. DAVIDSON METHOD OF CRACKING OILS Original Filed June 10 1920 2 Shets-Sheet 2- 3 C W arrow-vim EYM a liliozwmgs I Patented Jan. 1, rear.

Mrs

FAT .11 r orics.

' :osnrfi GEORGE nAvIDsoN, or PITTSBURGH, PENNSYLVANIA, AssIoNoa 'ro oH'ARLEs H. GONNER, or NEW YORK, N. Y. I I

METHOD or CRACKING OILS.

' Applicatlon"fi1ed June 10, 1920, Serial No. 387,967. Renewed October 24, 1922. Serial'No'. 596,685.

To all whom it may concern:

Be it known that I, J osnrrr Gnonon DAVID- soN, a citizen of the United States, residing 'at Pittsburgh, in the county of Allegheny, State of Pennsylvania, have invented certain new anduseful Improvements in Methods of Cracking Oils; and I do hereby declare the following to be a full, clear, and exact descriptionof the invention, such as will enable others skilled in the art to which it appertains to makeand use the same.

- This invention relates to an improved method for the thermal decomposition or cracking of oils, such as the higher boiling petroleum fractions, for the production therefrom of gasolene and other products.

In the cracking of petroleum oils,'for the production of gasolene, it has been proposed to. eifect the cracking by heating the oil in a closed retort by the application of external heat. In such procedures the effective heat must pass througn the walls of the still or retort, and the still walls must be heated to a much hi her temperature than that required for tilecracking operation. Moreover, the inner walls ofthe still, at the place where the heat is'applied, becomes coated with a layer of carbon, which interferes with the effective heat transfer and results in further overheating of the-still walls, causing buckling and warping of the still walls with consequent danger of explosion, particularly if the operation, is; carried out under ,a-high pressure. Moreover, such apparatus, the pressure which can safely be maintained in the still is limited, due to the weakening of-the still walls when overheated.

The present invention overcomes such ohjections and disadvantages and provides an improved method well adapted for use in v the thermal decomposition or cracking of oil on a commercial scale. According to the present invention, the heat necessary. for the cracking operation is generated by a heavy electric current of. low 'voltage passing through one or more massive resistors, pref 'erably of carbon, located away from the walls of the still, and such resistors are heated by an alternating current of suitable character to the temperature required for bringing about effective cracking of the'oil treated. The temperature of the resistors,

in the process of the resent invention, does not greatly exceed t e'temperature of the oil itself, althou h sufficient to heat the oil to the required temperature.- The heat .generated in this way is substantially all effective in the cracking operation and sub:

stantially all absorbed by the oil, the walls of the still remaining relatively cool and at a temperature which does not exceed that ofthe oil inside. The metal of the still therefore retains substantially its normal tensile strength, and the still is able to withstand correspondlngly higher pressures with safety,iwhereas the external heating of a still" to the temperature required for cracking, which is in the neighborhood of incip'ent'redness, decreases the strength of the still to about half its normal strength, and correspondingly reduces the internal pressure which the still can safely withstand. In the apparatus for carrying out the present invention, the massive electrodes are spaced away from thewalls'of the still a sufficient distance to prevent heating of the still walls by induction, even though a heavy current is'used. so that there is no cracking taking place where the oil contacts with the by subjecting them to, exceedingly high temperatures by means of an electric heater, such temperatures being exceedingly high as compared with temperatures commercially used. In the process of the present invention, however, the temperatures to which the oil is subjected do not exceed those commonly used in oil cracking operations, and the 'inwhich cracking operations are carried out.

In my investigation of the cracking ofoil by the application or heat generated by an thus found that the yield of gasolene 'ob-.

' rate of distillation.

electric current I have tound that the results obtained vary with variations in temperature and pressure as welljas with the rate of distillation and thev rate at which the electrical energy is supplied. These variousfactors are in'part interdependent and them selves capable'of some variation. I have tained increases with increase in pressure up to a certain point, beyond wh ch further increase 1n pressure does not result in corresponding increase in yield. In general,

the yield of gasoline increases with increase in pressure from around 100 pounds per square inch up to about 200 pounds per square inch, and I have obtained best results energy for preheating the oil.

with pressures around 160 to 200 pounds.

This increase in "the yield of gasolene due to increased pressure, results in a material de crease and economy in the electrical energy required per gallon otgasolene produced.

The rate of distillation, when the crack ing and distillation is carried out under a high pressure and at a corresponding temperature, likewise has an important influence in the result obtained. In the operation of the process of the present invention, the oil to be cracked is brought to the proper pressure by the passage of a heavy electric cur-- rent through the resistors and by confining ,the vapors until the pressure is built up to the required degree. The vapors are then released at substantially the same rate at which they are generated. in general, as the rate of distillation increases, the percentage of gasolene in the cracked material decreases,

altho the actualnumber of gallons of gasolene produced per hour generally increases. So also, the electrical energy necessary per gallon of gasolene produced varies with the For example, it the capacity or the retort or still in: gallons is divided by the rate of distillation in gallons per hour and the result obtained be considered the time'factor, then, as the time factor increases, that is, as the rateof distillation decreases, the energy necessary per gallon of gasolene produced will decrease until the time factoris in the neighborhood of one, that is, until the rate of distillatioii per hour is about equal to the capacity of the retort. If the time factor is still further-increased, that is, if the rate ofdistillation is still further reduced, the energy net gees tactor'will vary somewhat with variations in other conditions otoperation, but the investigations that-'lt liave made indicate'for -,best results that therateof distillation per though it will be evident that the rate of distillation is" capable of considerable variation. I

In the practicejof the present invention it is of advantage to preheat the on entering the crackingstill by subjecting it to heat interchange with the hot tdistillate thereby also effecting a-preliminary cooling of the distillate. This preheating of the oil entering the cracking still can be further supplemented if necessary so that the oil enters the still preheated to a temperature approximating that maintained in the still a d required for the cracking operation. 1e preheating of the oil in this way effects an important economy in the electrical energy required for the cracking operation,

and makes unnecessary the use of electrical.

The present invention is applicable to the thermal decomposition or cracking of ya rious oils or oi'l'lfractions, more particularly the higher boiling fractions of petroleum oils, either of the paraffin or asphaltum or mixed base series,- for the production therefrom of gasolene and other products; It is one advantage of the'proce ss of the present invention that the amount of permanent gas. produced is very small, While the amount of gasolene is relatively large, and the other products of the process are themselves for the most part of lighter gravity thanthe original oil. In general, the heavier fractions of petroleum,-when treated according to the present invention, give higher yields of gasoline at the same expenditure of electrical energy than the lighter fractions, that is, heavy gas oil or heavy paratlin oil gives higher yields of gasolene than light gas oil. The residueremaining afterthe distillation of the gasolene from the cracked material can be again subjected to the crack- I ing process, but the yield of gasolene produced is materially lower and the electrical energy required per gallon'of gasolene pro duced is higher than in the case of the origi nal higher boiling petroleum fractions, such as heavy oil or heavy paraliin oill The invention will be further described in connection with the accompanying drawings which show, in'a more or less conventional and diagrammatic manner, various forms of apparatus adapted for the practice of the process of the invention; but itisintended and will be understood that the invention is illustrated by, but not limited to, the specific embodiments so illustrated and described. i

In the acompanying drawings I Fig. 1 is a diagrammatic illustration of one-form of apparatus, Fig. 2 is a plan view of the cracking still of Fig. 1;

Fig. 3 is a detail View of one of the insulating bushings through which the leads are introduced; and

Figs. 4 and 5' are diagrammatlc viewscolumn or tower 4, and end covers or heads 5 through which access may be had to theinside of the still. Within the still are the massive carbon resistors more fully described. A pyrometer well for. determining the temperature of the oil in the still is indicated at 7.

From the reflux tower 4 the distillate passes through the pipe 8, having a regulat ing valve therein, to the heat interchanger 9, where a part of the distillate may be condensed and withdrawn through the valve control pipe 10, the rest of 'the distillate passing from the valve control pipe 11 to the condensing coil 12 surrounded by water or other cooling agent. From the condens ing coil the liquid condensate together with any unoondensed vapors pass through the valve controlled pipe 13 to the receptacle 14, from which the liquid can be withdrawn through the valve controlled pipe 20 and any residue deposited therein through the valve controlled pipe 19. The uncondensed' vapors pass from the valve controlled pipe- 15 to the, receptacle 16 and thence through i the valve controlled pipe 17 to theburner 18 where the 'uncondensed gas is burned to assist in the preheating of the oil before it enters the still.

The oil is forced by the pump 21 through the heatinterchanger 9 and thence through the pipe 23.to the preheating coil and thence through the pipe 2 to the still. The

oil will be preheated in the heat interchanger 9 by the hot distillate passing-therethrough and the oil thus preheated can be still further preheated in the coil 24: by the ac- It is advantageous, as abo-vepointedout, to preheat the oil to a temperature approximating that of the oil in the still preferably 'to a temperature of around 400 to 800 F., depending upon the grade of oil being cracked, so'

that little electrical energy will be needed the still to raisev the oil to the required temperature'for the cracking operation.

6, hereinafter- It will be evident that the oil should be I forced into the still, by the pump 21, at a pressure as great as that maintained within the still, which. temperature, as above noted, is capable of considerable variation.

Ingeneral, pressures lower than pounds and hlgher than 300 pounds are less advantageous, and I have obtained best results at temperatures around 160 to 200 pounds.

The pressure is regulated by means of one or more of thevalves in the pipes'8, 11, 13,

15 or. 17. "That is, the pressure may be main- -tained in the still by-means of the valve 8,

so that the subsequent condensation will take place at a lower pressure, or it may be maintained by means-of the valve in the pipe 13 or the pipe 15 or the pipe 17 so that the entire condensing system will be under the same pressure as the still. The construction and arrangement is such that a part orallo'f the condensing system can be keptunder still pressure or under lower pressures.

The vapors produced'n the still under the pressure maintained therein will pass up the refiux column 4 which is exposed tothe atmosphere and where 'any heavy material will be condensed and returned to the still. The unconden'sed vapors will then go" to the heat interchanger 9 yielding up part of their heat to the incomlng oil and in part condensing to forma condensate. which may be'removed from time to time through the pipe 10- while the still uneondensed vapors pass to the. condenser 12-as above described. The valve in the pipe 15, or the other valve or valves in the system which control the pressure are preferably so regulated to permit of the permanent gas to escape at the same rate that vapor is generated in the cracking still, thus maintaining the pressure in the system approximately constant.

The' heating of the cracking still is effected by the action of the massive resistors.

6 which are in turn heated by'alternating current. 7 These resistors are preferably of graphite or amorphous carbon, although other suitable material canv be :used in their.

construction. They are of such massive construction as to permit the necessary cleaning thereof without'removal from the cracking .still. -The massiveronstruction of the'electrodes permits a very heavy current to 'be carried, for example, a current as high as 20,000 amperes or higher. The massive construction of the electrodes permits themto be self-supporting andv gives them great strength and rigidity. so that they can be used for long periods of time without danger of breaking even with repeated cleaning-in a manner hereinafter described.

- These resistors in the apparatus illustrated in-Figs. 1 and 2, are three in number, and'connected together at one end by the connector 25 and at the other end by means of connectors 27 with the leads 26 of copper or other suitable metal. The connector-'25, which may be a copperibar, and

the copper leads 26, are so proportioned and connected that they will carry the current without danger of being heated to excessively high temperatures, 1

,-Where the resistors are of massive con- ,struction and are intended to carry a very heavy current, it is important to arrange them remote from the walls of the still, both 7 to protect the walls of the' still .and to prevent short-circuiting by the growth of car-. bon deposit upon the resistors' until --it touches the still walls. If the resistors are in close proximity to the walls of thestill jectionable carbon deposit on the still walls.

So also, as the cracking operation progresses, carbon is deposited to a greater or less extenton the electrically heated resistors, and,

if the resistors are in close proximity to the wallsof the still, the growth of carbon deposit will tend to connect the resistors with the still, thus'shortcircuiting the heating device and 'cai'ising the current to pass in part through the still walls.

- The proper construction and arrangement of the resistors is accordingly of importance where heavy currents are employed, while heavy currents are themselves important to obtain proper cracking and distillation due to the heat supplied thereby. FOP'BXZLIIlPlG, the investigations that I have made indicate that with the use of currents in the neighborhood of 2,000 amperes, thedistillation rate is only about to gallons per hour, which is too small for commercial operations unless the number of units were unreasonably multiplied. However, with a still of the construction illustrated in Fig, l,

with massive resistors carrying a current of 20,000 amperes, the cracking operation can be carried. on at the rate of from 200 to 350 gallons per hour; while with apparatus of larger size containing a plurality of heating devices .of a similar character either in a still of larger construction or in separate individual stills, the yield or output can be corrcspondmgly increased.

The proper arrangement of the leads or connectlons for the resistors is also of im- ,portance, where heavy currents are em- .pl'oyed, in order to avoid objectionable losses of electrical energy due to impedance and hysteresis. With alternating current, and with the heavy amperage which I emopposite ends of the cracking still. v,evenby introducing the leads of the alternat-ing current, whether single phase or polyplo ypa. very considerable percentage of the total electrical energy would be lost if the proper electricalconnections were not made,

for example, if the leads were introduced at How I moved.

remote phase, at the same location, these losses are reduced to a minimum, and the current effectively'applied in' the resistors themselves. It will thus be seen, from Figs. 1 and 2,

that'the three leads 26 of the three-phase alternating current supplied, enter the stillv sures maintained in the still and prevent leakage or escape of vapors therefrom. A suitable form of insulation and stuffing box is illustrated in 'Fig. 3. .In this figure the plate or portion of the still wall through which the leads pass is indicated at 30, and has welded thereto a tubular projection 31 externally threaded near its outer end. The copper lead 26 is closely wrapped with thin sheets of mica 32 which extend below the lower end of the extension 31 and beyond the outer end of the clamping nut 33 so that the lead is insulatedby the mica both from the member 31 and the nut 33. Asbestos packing 34 is inserted in a recess in the bushing 31 and the nut 33 is thenscrewed down to clamp the asbestos packing 34 in place and form a tight joint, holding the mica sheets firmly against the coppenlead' andpreventing escape. of vapors from the still. With construction and arrangement of this kind, pressures of around 200 pounds or more can readily be employed without danger of leakage around the leads and while still obtaining the necessary insulation for the heavy currents employed.

. The plate 30, and also the'ext'ension 31, are

deposit will become so great that it may seriously interfere with the operation of the electric heating device unless it is re- Itis not feasible to take the still apart and remove the resistors for the purpose of' cleaning them, inasmuch as this would involve cooling the resistorsto a sufa ficiently'lowtemperature to permit them to be exposed to the atmosphere, and inasmuch as the massive electrodes are not readily removed and would require a considerable period of time before they and having hand-wheels 0r gears 39 forcould be safely removed. Accordingly, provide for the cleaning of the resistors without removin themfrom the still. This may be effected by removing one of the heads 5 ,and inserting .a cleaning or scraping device for scraping the deposited carbon from the resistors; This can be done without permitting the still to cool and without any considerable loss of time for the cleaning operation.- It ismore advantageous, however, to provide cleaning means within the still itself which can be operated periodically. without opening .the still. Such cleaning devices are illustrated in Figs. 4 and 5, in which corresponding parts are indicated by the same reference numerals as in Fig. 1, with the sufiix.b.

and cappended thereto.

In the construction of Fig. 4, the' cleaning device consists of a series of thin sharp-edged metal bars, equally as .long as the resistors and of somewhat greater height. There are two of these bars'35 for each resistor and they are all united at each end and supported by cross-bars 36 which are in turn suspended by rods 37 passing through stufiing boxes 38 raising and lowering them. When excessive amounts of carbon have been deposited uponthe resistors, the current is interrupted and the gears or hand-wheels 39 are turned at the same rate and'in such a way that the bars 35 will be caused to rise parallel to the face of each resistor and only the fraction of'an inch distance from it. The deposited carbon is thus brushed or broken from the resistors and falls to the bottom ofthe still. v This cleaning movement can be repeated one or more times, after which the cleaning device isvlowered to its original position, the current is .again turned on, and the operation continued.

In the construction of Fig. '5, the cleaning device is operated by means of electro-magnets 40 having ironcores 41- secured to the lifting rods 3 passing to the electro-magnets, and the cores and lifting rods are suitably enclosed, as in a steel tube, to enable the pressure in the still to be maintained. When it is desired to operate the cleaning device, the'heating current is interrupted, and a suitable current of electricity is caused to pass through the electro-magnets40. the magnetic field thus produced causing the iron coresto rise and carry with them the cleanin device which will operate as above descri ed. On interrupting the magnetizingcurrent of the 'electro-magnets, the cleaning device will resume its position of rest below the resistors. The heating current is then re-established'through the resistors and the process proceeds as before. It will be evidentthat the provision of The rods 37 pass throughloose bearings havinglwater-cooled devices 42 arranged to keep-the heat of the stillfrom' cleaning devices for the resistors enables these resistors to be maintained inoperation for long periods of time,,- with only infrequent stopping in operation forcleaning,

and that such cleaning is effected without openin the stillfand without the necessity for coo ing of the still or of the'resisto'rs.

As the cracking operation proceeds, the amount of heavy residue and suspended carbon will increase, and it will usuallybe desirable'from time to time to withdraw the heav sludge and suspended carbon including t at broken off by the resistors. This is accomplished by opening the drawofl' pipe 3, after which thepipe is closed and afresh charge of oil introduced'into the still.

In the operation of-the still, the massive resistors 'willlbe maintainedeompletely sub- -merged in the oil,,whichshould preferably be maintained at such a levelthatthe still is about two-thirds ful'l. It will be noted that the horizontal arrangement-pf the still gives a large surface of contact between the oil and the vapor therein, which is advantageous, and that this arrangement also provides a; large vapor space within the still The oil within the still is a above the oil. subjected-to the heating action of the massive resistors, and is thereby heated to the cracking temperature, which will usually be between 700-and 900"v F., although the particular' temperature will vary with different oils. Inasmuch as the resistors themselves are completely immersed in the oil, they will be subjected to the cooling action of the oil in the still so that the resistors will be kept submergedtn the oil.

"In Figs'. 1 and '2 the heating is effected by three-phase alternating current supplied from the transformer 29 through the leads 26 to the three resistors 6. By using a threephase current, each lead and each resistor will only carry a third ofthe total current, for example, 6666 amperes where the total of 20,000 amperes is used. This arrangement permits the use of smaller leads and distributes the current in a particularly advantageous manner. The cleaning, devices,

of the character illustrated in Figs. 4 and- 5, are omitted from-the construction of Fig. 1, but even where such cleaning devices are i not provided, the massive resistors can nevertheless be cleaned by removing one of heating surface is provided, and since *this' surface is in intimate contaotwith the oil. it'is itself cooled by the oil; Theheat is thus of either the oil or resistors;

the apparatus.

the end plates 5 and inserting a cleaning device from outside, asabove described.

A poly-phase current, such as the thrpephase current illustrated in Figs 1 and 2, or the two-phase current illustrated in Figs. i and 5, is particularly advantageous and is to be more particularly recommended.

A single-phase alternating current can, however, be used, although with less advantage. Where such a single-phase current is used, the lead should. advantageously be introduced at the same location, the same as When a poly-phase current is used, for

reasons previously stated, namely, to avoid the large losses of energy due to hysteresis and impedance Which would result if the lead ,Were introduced The resistors themselves may vary insize and shape, but in. general'they should ad'- vantageously be'of a considerable height and.

.still Walls and provided with leadsof suitable constructionarranged :so'. that they enter the still at the same location. With re rial treated and the manner of operation;

sisters of the character described, a large efiectively supplied ,to' the oil,'through the resistors without objectionable overheating In the practice of the processofthe'pres ent invention, I recommend particularly the use of poly-phase current, such asthree-. phase current, which is economical and readily obtained, and the use of a heavy current of low voltage, for example, a current bf 15,000 to 20,000 amperes, and 20 t'o' 50 volts, and with massive resistors of slab- -like construction, having-a large heating surface in contact with the oil, andarrange generally to be recommended for commerto operate in the manner above described. A pressure of around 150 to 200' poundsis 'cial practice, inasmuch as such pressures give greater yields of gasolene with smaller expenditure of energy per gallon of' gaso'' lene produced, while apparatus can readily be constructed capable of withstandingsuch pressures without danger. I also recommend such a rate of distillation that the time'factor, that is, the'still capacity in gallons divided by therate of distillation in gallons per.'hour, be maintained around 0.8 to 1.0, since at this rate there is an approxiat opposite ends ofmation to themiiiimum. expenditure of ener-' gy pergallon of gasolene' produced. A more rapid rate of distillation may, however, be

more; advantageous where a greater number i of actual gallons of gasolene per hour is more important and where the other prod- -ucts of the cracking operation, mainly keros'ene, are of equal or greater value than the material originally treated." it also recommend that tlieoil be preheated in ah-eat eX-' changer-and in a. preheating coilvto a tem peraturebetiiveen600and 700? F. before it is introducedinto the still so that little energy will beiieeded in the still to raise the oil to the required temperature. 7

The resistors should-fbe proportioned to carry current; enough so that the contents of the retort will distill over in from about toils;- hours, but for-continuous operation it-will be understoodfthatF-the.o il is supplied at. substantially the rate'of distillation to; I

maintain the proper amount of oil inthe It is also advantageous to withdraw still. the heavy sludge and carbon periodically and at the time of cleaning the resistors or immediately thereafter and before the current is again turned on. The carbon broken or scraped off from the resistors can thus be removed together with the heavysludge and a fresh charge can then be introduced into the still sothat the cleaned electrodes operate upon fresh oil. Such periodic cleaning and withdrawal of sludge will be more or less infrequent, depending upon the mate but ordinarily cleaning will not be required until after the still has been in operation for several hours and with some oils the still can operate for relatively long periods of time before cleaning will be necessary.

From'tlie foregoing description, it will be seen that the present invention provides an improved method Well adapted for commercial operation, and that the invention presents various features of advantage and of novelty. The cracking operation is carried out with internal heating elements, heated by electricity, but' with such size and construction of the heating elements and with such regulation of the current supplied thereto, that-the oil is rapidly and effectively heated to the cracking temperature without objectionable overheating. The v current supplied may thus be a heavy current,;but owing to the massive character of the resistors, the heating effect of the heavy current is utilizedin heating the oil, without objectionable overheating of the resist.-- ors. In fact, as above noted, the resistors have been found to have a relatively low temperature not greatly exceeding the temperature of he oil itself.

I It will also be noted that the process of the present invention involves the treatment of relatively large bodies of oil within which present invention,'as hereinbefore pointed the resistors are submerged, as distinguished from processes involvin a flow of 'oil past r ors act directly upon the liquid oil ,and "in 'but nevertheless with rapid and effective which the oil itself is kept in intimate contact. with the resistors and actually penee trates the porous surface of the carbon resistors,.as distinguished from operations involving the use of such hi-gh temperatures that the oil can exist only in a vapor state at the temperatures of the heating elements or surfaces. Owing to the intimate heating efi'ect obtained according to the present invention, the crackingoperationcan be effected without violent ebullition of the oil,

cracking thereof.

It is a characteristic advantage of the out, that the amount of permanent gas producedis very small. Ihave thus obtained effective cracking of the oil with the conversion of as little as 1% or less of the original oil into permanent gas. It is also a characteristic advantage of the present invention that, with increased-yields of gasolene due to increased pressure, the gas loss does not correspondingly increase, but remains only a small percentage .of the original oil, even where the amount of gasolene produced is as high as 35 to 40% or more of the original oil.

I do notclaim herein the improved apparatus herein described, inasmuch as such apparatus formsthe subject matter of a separate application.

I claim:

1. The method of cracking oils, which comprises immersing in the oil one or more massive electrical resistors, supplying polyphase alternating current thereto to heat the oil to a cracking temperature and pressure, and regulating the current so that the temperature of the resistors does not greatly exceed that of the oil with which they are in intimate contact.

2. The method of cracking 1 oil, which comprises immersing in a relatively large body of oil a plurality of resistors of massive construction connected with sources of poly-phase alternating current and heating the oil by means of such resistors to the cracking temperature and pressure.

3. The method of cracking oil, which comprises subjecting arelatively large body of oil to the heating action of massive resistors heated by poly-phase alternating current to the cracking temperature, maintaining the resistors submerged and inintimate contact with the oil, and supplying further amounts of oil to' make up for that which is cracked and distilled.

4. The method of cracking oil, which comprises heating the same by means of submerged electric resistors of massive construction to the cracking temperature by means of poly-phase alternating current and regulating the rate of cracking and distillation, at a pressure of-about to 200 pounds per square inch, so that the contents of the still wilLbe cracked and distilled in a period from aboutone-half hour to one and onehalf-h'ours, and supplying further amounts of oil to make'up for that which is being cracked and distilled.

v 5. The method of cracking oil, which com prises heating thesame by means of sub merged electric resistors of massive con-v struction to the cracking temperature by means of poly-phase alternating current and regulating the rate of cracking andv distilla- 6. The method of cracking oil, which comprises preheating the oil to a temperature below the cracking temperature, sup-- tion-,at a pressure of about 100- to 200 pounds per square inch, so that the contents ofthe H plying-the preheated oil to the-cracking still and heating the same therein to a cracking temperature and pressure by means of sub merged massive electric resistors heated by poly-phase alternating current, and circu lating the vapors resulting from the cracking operation into heat interchanging relation with the oil entering the still, thereby preheating the oil and cooling the hot vapors. a

7. The method of cracking oils, which comprises immersing in a body of the oil massive electric resistors heated by alternating current to the cracking tem erature and periodically removing the car on deposit from said resistors without thereof from the still.

8.- The method of cracking oil, which com prises confining a relatively large body of oil in a cracking still, immersing in-the oil one or more electrical resistors of massive construction, and supplying alternating current to said resistor or resistors through leads entering the still at one locality to heat the same to the cracking temperature.

I 9. Themethod of cracking oil, which comprises confining a relatively large body of oil in a cracking still, immersing in the oil removalelectrical resistors of massive construction,

and supplying a heavy poly-phase alternating current to said resistor or resistors to heat thesameto the crackiu temperature,- the current being so regulated that the temperature of the resistoror resistors does not Lark moving-the carbon deposits from'said resistors Without cooling of the still or re- J 4 nemperature andpressure by means of submerged resistors of massive structure heated by alternating current and periodically removing the carbon depositsfiromsaid resistors Without removal of. the resistors therefrom and Without opening the still or reducing the pressure therein.

ture.

JosEPH' enonen DAVIDSQN.

In testimony whereof I affix my signa- 

